I. Field of the Invention
The present invention relates generally to methods and devices for the monitoring, measuring, and evaluation of internal combustion engine operation. The present invention relates more specifically to a method and apparatus for sensing, measuring, and analyzing the operation of an internal combustion engine by detecting mechanical stress pulses created by both the combustion process and the mechanical action and interaction of the engine elements. The present invention in particular applies to both a one-time, non-destructive evaluation of engine deterioration and an on-going, on-board, monitoring of engine operation.
II. Description of the Prior Art
Information regarding the operation and condition of internal combustion engines is desirable and important from two standpoints. First, the designs of internal combustion engines are constantly being refined to improve efficiency and output. Factors which affect efficiency and output are sometimes difficult to control, measure, and analyze, especially during the operation of the engine combustion cycle. If detailed information on the timing of combustive events, the operation of the mechanical components, and the combustion characteristics, could be obtained then a much more thorough efficiency and condition analysis could be achieved. From a second standpoint, assuming some internal combustion engine of optimal efficiency and output, the inevitable and on-going deterioration of the engine and its effect on the efficiency and output, is of great importance. If information could be gathered and analyzed on a continuous basis, many deteriorating actions and effects within an engine could be detected as it operates and, in some cases, compensated for or brought to the attention of the engine operator in advance of significant detrimental effects on the operation of the engine.
A more thorough knowledge and understanding, therefore, of the activities and occurrences within an internal combustion engine would help lead to not only improved engine designs but also to the better use and operation of existing engine designs. Efforts thus far in the field to obtain relevant information on the operation of the internal combustion process have been limited to somewhat gross measurements of temperatures and pressures within the engine. Typically, as for example in an automotive engine, lubricant pressure and temperature, coolant temperature, and combustion cycle timing, have been the extent of the monitoring. In more refined applications, analysis of exhaust gases, spark plug firings, and periodic wear measurements have provided additional bits of information from which to discern and describe the function and efficiency of the engine. On the whole, however, very little has been done in the field to obtain the much-needed, yet more difficult to obtain, information associated with the operation of the mechanical elements and the combustion of the fuel within the engine. This is not surprising, since the environment within and about an internal combustion engine is not conducive to the sensitive types of sensors that are normally required to obtain the more detailed information about engine performance. Combine this problem with the higher costs associated with the more refined sensors, and it is easy to understand why little effort has been made to acquire additional details about engine operation along these lines.
As indicated above, well-known parameters that can and have been measured for engine operation include various temperatures and pressures whose values are obtained through thermocouple-based sensors or more rugged but less sensitive pressure transducers. Since the operational temperatures and pressures within an engine are an indication of its efficiency and can ultimately be an indication of problems occurring in the engine, these parameters are quite important but somewhat limited in the information they convey. More often than not, changes in temperature and pressure parameters merely indicate the presence of a problem or an operational inefficiency and do nothing to suggest where that problem might be occurring or what the basis of an inefficiency is.
More sensitive types of transducers have been utilized in the laboratory to analyze engine conditions but very little of this laboratory analysis has been translated into an on-board operational analysis or monitoring. In the laboratory, piezoelectric transducers have been able to detect, monitor and assist in the analysis of not only pressure characteristics (and when operated in conjunction with thermocouples, temperature characteristics) but also the mechanical interaction of the components of the engine itself. Piezoelectric transducers can be configured to measure pressures within the combustion chambers, the lubricant system, and may also be used to localize mechanical events in a manner that allows some indication of their general location. Piezoelectric transducers, however, though rugged for many applications, are still far too delicate to be utilized for long periods of time in association with the high operating temperature and vibrational effects within and about internal combustion engines. In addition, the ability of piezoelectric transducers to finely distinguish vibrations and waves that might be associated with anomalous events and/or ordinary events in the operation of an engine is quite limited.
It would, therefore, be advantageous to develop an apparatus and method for detecting, measuring, and analyzing conditions within an internal combustion engine with a sensitivity that allows a more thorough understanding of not only ordinary operational events but also any anomalous events within the engine that might occur over short or long periods of time. It would be desirable to have such a system that could, on the one hand, function in an analytical setting where the then existing condition of an engine could be determined and characterized. On the other hand it would also be advantageous if such an apparatus and method could be implemented in a monitoring mode whereby information on the on-going, long-term operation of an engine could be collected and retained for either later analysis or for continuous comparison with threshold values that might signal problems. Further, it would be advantageous to have such a method and apparatus that would permit feedback compensation for events where such compensation can be shown appropriate and where the event is a modifiable occurrence.
Some use of more recent sensor technology and devices such as magnetostrictive sensors has been shown in other fields to provide sensitive means for mechanical stress wave measurement in both metallic and non-metallic structures and machines. Some application of these magnetostrictive devices has been made in the field of internal combustion engines and might be typified by the following:
U.S. Pat. No. 4,736,620 issued to Adolph on Apr. 12, 1988, entitled, "Magnetostrictive Element for Measuring Knocking Engines," describes the use of a magnetostrictive element to detect self-ignition or "knocking" in the combustion cycle. A number of sensor devices are connected by way of mechanical wave guides (wires) to each of the individual combustion chambers within an engine. The ability of these devices to gather information, however, is strictly limited to the detection of knocking within a specific cylinder and over all does not lend itself to easy installation on existing engines or, for that matter, versatility in its ability to characterize any engine events other than the occurrence of combustion.
U.S. Pat. No. 4,463,610 issued to Anderson III, et al on Aug. 7, 1984, entitled "Tuned Vibration Detector," describes a sensor for detecting engine knock that incorporates a tuning mechanism mechanically resonant with a pre-selected vibrational frequency. The effects of engine knock on the tuning network in the Anderson device indicate the varying applied stress. The limitations described above with respect to the Adolph patent, however, likewise apply herein, insofar as little more than a detection of engine knock as an event is possible with such a sensor.
U.S. Pat. No. 2,534,276 issued to Lancor on Dec. 19, 1950, entitled "Vibration Pick-up Device and System," describes an early magnetostrictive-type vibration sensor utilized to detect impact, shock, or detonation, and which functions much like an accelerometer. This device is mounted in an engine's cylinder wall. Here again, the device is limited in that it isolates only what goes on in a single combustion cylinder and, even then, gathers information relevant only to the occurrence of a combustive event, and little more.
While the above patents represent that some effort has been made to utilize magnetostrictive-type sensors in engine analysis, it is clear that such uses to date have been quite limited. These limitations derive from the fact that the sensor structures and methods disclosed heretofore are unable to isolate and interpret anything other than the gross occurrence of a combustion event. The fact that efforts in the past have resorted only to identifying combustive events and their relative time spacing, and that these sensors must be associated with specific individual combustion chambers, indicates that little more information can be obtained under the constraints placed on them.
III. Background on the Magnetostrictive Effect
The magnetostrictive effect is a property peculiar to ferromagnetic materials. The magnetostrictive effect refers to the phenomena of physical, dimensional change associated with variations in magnetization. The effect is widely used to make vibrating elements for such things as sonar transducers, hydrophones, and magnetostrictive delay lines for electric signals. The magnetostrictive effect actually describes physical/magnetic interactions that can occur in two directions. The Villari effect occurs when stress waves or mechanical waves within a ferromagnetic material cause abrupt, local dimensional changes in the material which, when they occur within an established magnetic field, can generate a magnetic flux change detectible by a receiving coil in the vicinity. The Joule effect, being the reverse of the Villari effect, occurs when a changing magnetic flux induces a mechanical vibrational motion in a ferromagnetic material through the generation of a mechanical wave or stress wave. Typically, the Joule effect is achieved by passing a current of varying magnitude through a coil placed within a static magnetic field thereby modifying the magnetic field and imparting mechanical waves into a ferromagnetic material present in that field. These mechanical or stress waves then propagate not only through the portion of the ferromagnetic material adjacent to the generating coil but also into and through any further materials in mechanical contact with the ferromagnetic material. In this way, non-ferromagnetic materials can serve as conduits for the mechanical waves or stress waves that can thereafter be measured by directing them through these ferromagnetic "wave guides" placed proximate to the magnetostrictive sensor element.
The advantages of magnetostrictive sensors over other types of vibrational sensors becomes quite clear when the structure of such sensors is described. All of the components typically utilized in magnetostrictive sensors are temperature, pressure, and environment-resistant in ways that many other types of sensors, such as piezoelectric based sensors, are not. High temperature, permanent magnets, magnetic coils, and ferromagnetic materials are quite easy to produce in a variety of configurations. Further, although evidence from the previous applications of magnetostrictive sensors would indicate the contrary, magnetostrictive sensors are capable of detecting mechanical waves and translating them into signals that are subject to very fine analysis and discrimination in a manner that allows information to be obtained from the elements in an engine that have initially generated the stress.